1. Field of the Invention
The present invention relates to an image processing apparatus such as an image reading device that scans an image of a document or an image forming apparatus including an image reading device.
2. Description of the Related Art
A technology called marking, typical example of which is a barcode, has been available.
With this technology, a document printed with a specific pattern can be scanned, and information represented in a pattern extracted from the image thus scanned can be taken out.
Such a technology is currently used in various applications.
For example, often found on a label on a product or a publication is a barcode (Quick Response (QR) code (registered trademark)) for guiding a user to a web site related the product or the publication.
A background pattern for indicating that copying with a copier is permitted or prohibited is also used in office documents.
A barcode is a pattern that occupies a local area of a document, whereas a background pattern is a pattern composed of a large number of small dots or lines superimposed with the content of the document. Both of these patterns can be said to be “distractive” to a user viewing the label, the publication, or the document.
It is because a pattern understood by a machine is mixed with a piece of content (characters or shapes) viewed and understood by a human on the same page.
In order to make a pattern such as a barcode or a background pattern in the content of a document not “distractive”, such a pattern can be printed with a toner (ink) of a less visible color, for example.
Recently, it has become possible to use a clear toner in the electrophotographic process in an image forming apparatus such as a facsimile, a printer, a copier, or a multi-function peripheral (MFP). In this context, the clear toner is considered as an alternative for making a pattern such as a barcode or a background pattern in the content of a document not “distractive”.
A pattern such as a barcode or a background pattern can be made not “distractive” if the pattern is printed using a clear toner, but then extraction of the pattern becomes an issue.
To explain further, an image reading device (scanner) for reading the image of a document is incapable of reading a pattern formed with a clear toner that is not visible to a human.
This is because a general image reading device is designed to acquire an image having the same appearance as that observable by a human.
Therefore, such an issue cannot be addressed unless such a design is somewhat changed.
As solutions addressing such an issue, following technologies have been disclosed.
(1) Technology Mixing Special Material to Clear Toner
These include technologies disclosed in Japanese Patent Application Laid-open No. 2005-170007 and Japanese Patent Application Laid-open No. 2001-265181. In the technology according to the former disclosure, an image is formed on a document with a fluorescent ink that becomes fluorescent under ultraviolet. The document is then irradiated with ultraviolet, and the image is detected via the light emitted from the fluorescent ink. In the technology according to the latter disclosure, an invisible image is formed on a document using a recording material having an absorption range for invisible light. The document is then irradiated with invisible light including infrared, and the invisible image is detected based on the portion where the light is absorbed.
(2) Technology Increasing Gloss Using Clear Toner
An area applied with a clear toner has increased smoothness, and is glossy. An area not applied with a clear toner maintains low smoothness of the original paper, and is not glossy.
Therefore, in the technology disclosed in Japanese Patent Application Laid-open No. H06-070097, a binary pattern is observed from these areas by detecting a specular reflection. Such a technology produces an image that is visible to a human when viewed from a particular angle, but is not “distractive” as much.
(3) Japanese Patent Application Laid-open No. 2010-102032 discloses a technology that provides a charge-coupled device (CCD) for detecting diffuse reflections so that only diffuse reflections are detected, because the color of a document (wavelengths absorbed by a document) can be read more precisely by detecting diffuse reflections rather than a specular reflection.
The light amount of diffuse reflections increases or decreases depending on the color of a document (the color of the paper itself and the color of a toner or an ink attached to the paper) and the gloss level.
As illustrated in FIG. 9, there is a theorem that the amount of diffuse reflections with respect to incident light becomes smaller on a glossy area that is glossy in the document illustrated in section (b) in FIG. 9, compared with that on a non-glossy area without any gloss in the document illustrated in section (a) in FIG. 9, as long as the color of the document is the same.
This theorem is used in detecting a gloss pattern on a paper surface (portions to which no toner or ink is attached).
In the technology described in (1) above, a binary pattern image in which the light is absorbed by a different degree can be detected as long as such a pattern includes an area printed with a fluorescent ink (glossy portion) and an area not printed with a fluorescent ink. Furthermore, a fluorescent ink itself is not distractive because a fluorescent ink is transparent. However, because a special illumination and light receiving element covering a invisible wavelength range need to be provided to the image reading device, costs in manufacturing of the image reading device are increased, disadvantageously.
Although the technology described in (2) above is not intended for reading a gloss pattern (glossy portion), a gloss pattern can be read using a light receiving element for a specular reflection.
However, because a special light receiving element is provided to the image reading device, the system of the image reading device increases in scale, and costs in manufacturing of the image reading device are increased, disadvantageously.
In the technology described in (3) above, scanning is performed with an illumination having a certain light amount (85 percent of a common light amount), and brightness of a glossy area (glossy portion) and that of a non-glossy area are identified based on a frequency distribution (histogram) of the brightness values across the image thus acquired. Therefore, a special illumination or light receiving element does not need to be provided to the image reading device, and an increase of manufacturing costs of the image reading device can be avoided.
However, such an image reading device cannot accommodate with diverse paper types, disadvantageously.
That is, the image reading device might not be capable of detecting a pattern correctly depending on the whiteness of paper.
While the image reading device might be able to detect a pattern on a highly white paper sheet, the image reading device might not be able to detect a pattern on a less white paper sheet, because the brightness of the glossy area and that of the non-glossy area become too close to be distinguished.
Furthermore, none of the technologies described above does not provide means for fully taking advantage of the information represented in a glossy portion provided in addition to a normal image.
Therefore, there is a need for an image processing apparatus capable of achieving highly useful image processing that uses information represented in a glossy portion.